The present invention relates generally to the field of semiconductor processing equipment. More particularly, the present invention relates to a method and apparatus for detecting developer endpoint in a semiconductor processing sequence. Merely by way of example, the method and apparatus have been applied to detecting the endpoint during a develop process using reflectometry and scatterometry. But it would be recognized that the invention has a much broader range of applicability.
Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. As device geometries have become more dense, reductions in the spacing between device elements has occurred. The minimum linewidths achieved using semiconductor lithography systems, sometimes referred to as a critical dimension (CD) have decreased over time.
Lithography or photolithography generally refers to processes for transferring patterns between a mask layer and a semiconductor substrate. In lithography processes for semiconductor device fabrication, a silicon substrate is uniformly coated with a photosensitive material, referred to as a photoresist, in a cluster tool. A scanner/stepper tool selectively exposes the photoresist to some form of electromagnetic radiation to generate a circuit pattern corresponding to an individual layer of the integrated circuit (IC) device to be formed on the substrate surface. Generally, the photoresist film is selectively exposed using a mask layer that preferentially blocks a portion of the incident radiation. The portions of the photoresist film that are exposed to the incident radiation become more or less soluble depending on the type of photoresist that is utilized. A developing step dissolves the more soluble regions of the photoresist film, producing a patterned photoresist layer corresponding to the mask layer used in the exposure process.
The precision with which the patterns are developed on the semiconductor substrate impacts the CDs present on the substrate, likely impacting device performance. Overdevelopment may result in an increase in linewidths, whereas underdevelopment may result in portions of the photoresist layer not being removed as desired. Various methods have been used to determine the endpoint of the developer process, including visual inspection and trial and error process development. However, the utility of these methods has decreased as device densities have increased.
Therefore, there is a need in the art for improved systems for detecting developer endpoint and improved methods of operating the same.